Frequency and time allocation multiplex system



Dec. 29, 1964 P. DEMAN 3,163,718

FREQUENCY AND TIME ALLOCATION MULTIPLEX SYSTEM P. DEMAN Dec. 29, 1964 FREQUENCY AND TIME ALLOCATION MULTIPLEX SYSTEM Filed June 28, 1962 4 Sheets-Sheet 2 www!! SXT! wl wl mmc /A/vEA/TOE Pl ER RE 06M AIV ATTORNEY Dec. 29, 1964 P. DEMAN 3,163,718

FREQUENCY AND TIME ALLocATIoN MULTIPLEX SYSTEM /NVE/v T012 PIERRE @lf/WAN United States Patent 3,163,719 FREQUENCY AND TIME ALLCATION i MULTIPLEX SYSTEM Pierre. Deman, 56 Rue Fondary, Paris, France Filed June 28, 1962, Ser. No. 205,976 4 Claims. (Cl. 179-15) The present invention `concerns multiplex systems, that is transmissionjsystems capable of transmitting information signals over sub-channels comprised in a single channel.

Frequency allocation multiplex systems are already known, which are obtained by dividing the frequency bandwidth of a rnain transmission channel into a number of sub-channels, each sub-channel being allotted the task of transmitting a particular information signal. The subchannels are juxtaposed within the main channel. On reception, individual sub-channels are separated by lters. With these knownisystems, while it is desirable, for efficiencys sake, to pack the sub-channels as tightly as possible against one another, it is essential that the frequency juxtaposition be effected without frequency overlapping, in view of preventing inter-frequency sub-channel crosstalk. i

l Time allocation multiplex systems are already known,

l which consist in transmitting through a main transmission channel a `sequence of pulse signals which arermopdulated in cyclical permutation with a number of information signals, each corresponding to a sub-channel in said main channel. On reception,rindividual sub-channels are separated by time allocating or dividing devices. these known systems, while 'it is desirable for elliciencys sake i' to pack the pulses of the. sequence as tightlyras possi-ble Y against one another, it is seential that this juxtaposition be effected without time overlapping, in view of inter-time sub-channel cross-talk. i A

l The main drawback of pure frequency multiplex systems is that a severe vfrequency 4band limitation in subchannels involves the use of very long (theoretically infinite) signals. The main drawback of pure time multi- (theoretically infinite) bandwidth for the transmission line- The object of the present invention is Vto provide a multipleX system, operating as a frequency allocation multiplex system and characterized by the fact that the subchannels Vcorrespondingto the independent information signals present a certain amount of overlapping relatively to one another.'

. 'Another object of this invention is a multiplex system characterized by the fact that the elementary signals in a Vgiven sub-channel present a certain amount of overlapping with respect toV time.

These two objects respectively derive from a more general object, namely the utilization of elementary signals that are not orthogonal relatively to one another.

In brief,a plurality of information signals are recur-r` ,rently sampled and the samples applied to band-filters nal, the contributions are obtained'not only from `the i sample ofthissignal at'said given sampling instant but alsovfrom, samples "of the same at earlier sampling in-f stante.' Due .to the fact that theV Laplace transform isa 'linear operationythe samples of the composite signal are Wrelatedrto' samples kofthe information 'signals-atr a plu- There results that #L0 plex systems istliat they suppose the use of very large f "Ice rality of sampling Ainstants by linear relationships Vand consequently the sample of a given information signal at a given instant can be derived from samples of the composite signal at a plurality of sampling instants'by f -matrioal analysis. .t

According to the invention, a frequency and time allo- Vband-filter means having center frequencies spaced apart from one another and frequency pass-bands overlapping one another, said plurality of first resonant symmetrical band-filter means being equal in number to said modulation signal plurality, means for respectively applying said input recurrent modulated sample Vpulses to said first band-filter means and deriving therefrom elementary signals, said elementary signals having respectively as their carrier frequencies the center frequencies of said first band-filter means, as their bandwidth the pass-bands thereof and a time-duration comprised between u and (v-l-l) times the recurrence period of said recurrent modulated sample pulses and means for adding theelementary signals derived from said first band-filter means and applying the resultant signal -to a-single transmission channel; said receiver comprises a delay-line having an output recurrent samplesV whereby said ,uil output re- V current samples are related to ,uv input samples pulses 'applied at v recurrent sampling cycles to al first band-l lter means by a matrical constant coeliicient relationship, and matrix means having au lines connected `to said second band-filter means and ,te columnsfand crosspoint elements proportional to said Vconstant coeiiicients,

' 1whereby the modulation signals are restored at the outputs of said columns. v i Y, It is known that it is possible to double of the number of subi-channels in either time division multiplexsystems by vusing separateimphase @and quadrature sample pulses which, once amplitude-modulated, can be transmitted independently on the same line, the quadrature: pulses often called imaginary unit pulses being obtained by differentiation ofA thev in-phase pulses often called real unit pulses; in that case, appropriate in-phase and quadrature'demodulators must be provided in the receiver.

The new transmitting ,system hereinafter describedis adapted to make use of that property, as well.

, The invention Vwill -be described in greater detail withl reference to the accompanying drawing forming a part` of the specification and in which:

FIG. l isa block diagram Iof a preferred forml of mltiplex :communication transmitter system in accordance with the present invention; Y

FIG. 2 is a block diagram of apreferred form of multiplex communication receiver system in accordance with the present invention; v f

FIG,` 3a represents the pass-band characteristic curves of the filters used in thetransmitter and receiver andfshows that the center angularfrequenciesm1,. o2, p3 are spaced apart from one anotherand the pass-band are over-lapping one anothertFIG. 3b represents a particular4 waveform for an elementary .signal and shows1that the.y duration ofrsaid elementary signal is Yequal to three times the recurrence period r' of thesampling pulses; f

3,163,718 Patented Dec. 279, 1964 FIG. 4 is a block diagram of a second form of multiplex communication receiver system; and

FIG. 5 represents the circuit componentsof the matrix network of FIG. 2.

Referring now to FIG. 1 of the drawings, 111, 112, 113, 11'1, 112, 113 are six input terminals to which are applied separate information signals. Terminals 111 and 111 are connected to a pulse `modulator and filter unit 101 which comprises yan in-phase modulator or sampler 131, a phase-quadrature modulator or sampler 131 and a pass-band filter 141. The central angular frequency of iilter`141 is w1 and its attenuation curve is shown at 171 in FIG. 3a. In a similar manner, terminals 112 and 11'2 are connected to pulse modulator and filter unit 102 including samplers 132 and 132 and filter 142 and terminals 113 and 113 are connected to pulse modulator and filter unit 103 including samplers 133 and 133 and filter l143. The central angular frequencies of filters 142 and 143 are respectively m2 and w3 and the corresponding atten-y uation curves are represented at 172 and 173 respectively. The output terminals 121, 122, 123 of modulator units 101, 102, 103 are connected to the single communication channel 4 of the system through buffer amplifiers 51, 52 and 53.

c The sampling pulses -applied to samplers 131, 132, 133 are derived from a pulse generator 2 which will be called in-phase pulse generator. This generator is driven by master time-base 1 and produces recurrent very short pulses of ksubstantially rectangular waveform 52. ln-

chronizcd pulse generator type.

Thesampling pulses applied to samplers 131, 132, 133

are derived from a pulse generator 3 which will be called phase-quadrature pulse generator. This generator is also driven by lmaster time-base 1 and products two-pip pulses 53. Phase-*quadrature pulse generator 3 may be of the delay line type for example such as illustrated Fig. 5.5, page 2.100 of Principles of Radar, McGraw-Hill Book Co., Inc., 1946.

Pulses 52 have a waveform which is theoretically the unit impulse or Dirac function waveform S0 (t) with a finite amplitude. Pulses 53 have a waveform which is theoretically the so-called `doublet unit impulse Waveform S1 (t). The doublet unit impulse is therderiva'tive of the unit impulse. The unit impulse and the double unit irnpulse are represented in FIG. 3, right Vhand column, line n=0 and n=11, page 652 vof the article of Campbell in the Bell System Technical Journal, October 28, vol. 7, No. 4, entitled Practical Application of the Fourier Integr'al. These functions constitute the pairs 403 and 4-04 of Table I, page 667 of said article. These two functions are orthogonal with each other and this allows the number of uncoupled communication channels to be doubled. c

Filters 141, 142, 143 define frequency channels I, VII, III overlapping one another. The attenuation curves 171- 173(FIG. 3a) are symmetrical and show that frequency channel II'overlaps the 'two others. It may be said thatY the frequency channel overlapping ratio is three. Y

, Samplers 131, 132, 133 define time allocations A, B, C .1 of duration 'r 1/1- being the recurrence frequency of the master time-base 1. A sample 52'passing, after being modulated, through filter 141 gives rise to an elementary signal 54 having a duration which lasts several cycledurations 1- and it Will be assumed that the elementary signal duration is comprised between 3T and 4er. Thus, the number v above-referred to is here equal to three.

In the following, the samples of the information signal' c sampling cycle. Thus, the sample in channel of number set up during the/cth sampling cycle is denoted .r1-11.' The elementary signal derived from the sample x13 after it had passed through the filter inserted into input channel of order i will be denoted x13 :11111 where apk is a function of time which is nothing different than the inverse Laplace transform of the amplitude-frequency characteristic of the filter and will be explicited later. Already now, it can .be noticed that signal 54 has for its carrier frequency the center frequency of the filter fnom which it is issuing, for its bandwidth the pass-band of the filter and that its duration depends upon the damping factor of the filter. The composite signal in common channel 4 at a given instant, say 3T, is a linear combination of the three elementary signals derived from the three samples taken up at this instant from the information signals in the input channels, from the three samples at a sampling period before and from the three samples Iat Vtwo sampling periods before, i.e. a linear combination of the samples x11, x12, X13, x21, x22, x23, x31, x32, x33- FIG. 2 illustrates the receiving part of the system. The signal conveyed by transmission line 4 is applied to the input of a delay line 6 which is provided with a number of equidistant taps, three in the specific instance, designated as 61, 62, 63. More generally, this number is equal to the number u above referred to. The delay introduced by line 6 between t'wo successive taps is equal to one period T ofthe master time base 1.

Terminals 61, 62, 63 are respectively connected to the input terminals 1121, 1122, 1123 of three `demodulators units designated by 1101, 1102 and 1103 which are exactly yidentical with one another. Each demodulator unit, 1101 for example, comprises a buffer amplifier 1051, three filters 11411, 11421, 11431 respectvely identical to filters 141, 142, 143 of FIG. 1 and connected in parallel to the output of buffer amplifier 1051, and samplers 11311, 11321, 11331, 11311, 11321, 11331 respectively identical toy samplers 131, 132, 133, 13'1, 13'2, 13'3 of FIG. 1 and connected in parallel by pairs to the outputs of the filters. Samplers 11311 and 113'11 are connected to the ,output of filter 114.11; samplers 11321 and 11321 are connected to ythe output of filter 11421 and samplers 11331^and 11331 are connected tothe output of filter 11431.

The sampling pulses applied to samplers 11311, 11321, 11331 of demodulator unit 1101, to samplers 11312, 11322, 11332 of demodulator unit 1102 and the samplers 11313, 11323, 11333 of demodulator unit 1103 are derived from in-phase pulse generator 102, identical with in-,phase pulse generator 2. The sampling pulses applied to samplers 113'11, 11321, 11331 and to the similar samplers kin demodulator units 1102 and 1103 are derived 'from phase.-

quadrature pulse generator 103, identicalgwith phase` 1 quadrature puise generator 3. Both generators 102 and 103 `are driven by time-base 101 synchronous with miaster time-base 1. For synchronization purpose, a -`signal is sent by time-base A1 to timefbase 101 and this signal is :assumed to -be Vpositively outside the bandwidth occupicd by the frequency sub-channels. It passes through buffer amplifiers 5.1 and 105,1.

Demodulator unit V1101 has six outputs, the rst three 11111, 11121, 11131 being relative to samples produced by means of unit impulses andthe latest. three 11111, 11121, 11131 being relative to samples produced by means of doublet unit impulses. The reference numerals of the outputs of demodulator unit 1102 are derived from the reference numerals of the loutputs of demodulator unit 1101 by substituting second subscript 2 for ser ond subscript l and those of demodulator unit 1103 by substituting second subscript 3 for second subscript l.

The eighteen outputs of demodulators 1101, 1102, 1103 are connected to a matrix network 20 which `hassix outputs 2111, 2112, 2113, 2111, 211'2, 2-11'3 Ycorresponding respectively tollinputs 111, 112, 113, "1 11', 11.2,:11'3; i

amavis formation signals of which are sampled by doublet unit and the inverse Laplace trausformt impulses will be provisionally disregarded;V Y v w sin w w sin t Let us assume that filters 131, 132 and 133 of the modulaf1 2: 1( t) =x11efIt for 'units and fina-S 11311, 11321, 11321,'211312, 11322, d1-w22 Y 11332, 11313, 11323, 11333 ofthe demodulator unitsrare This equatlon may bewritten in a moresymmeitric form:

R-L-C circuits having the vsame attenuation` factor R/2L=a and central angular frequencies w1 as regards sin @i cos ET'w'zt 2 filters 131, 11311, 11312 and 11313, (1)2 aS fegal'ds-1te1s f1,2;1(t) :Ine-at t 132, 11322, 11322 and 11.323 and 22 as regards uers 132, Q F92 Y 11321, 11322 and 11322. y v y sin cd1-@2t cos'ewzt The response of filter 131 toa short pulse of amplitude 2 2 x11 may be considered as the response to`x11S(t), where Y w1-w2 S0(t) is the unit impulse. The Laplace transform of andb nel tin t' Said response is: Y 60 g (w1 wz) with respect to (w1-hwg), 1e

the first bracketed term' with respect to the second:

v 9311001 t 15 i Fm) :mz-LT@ .sin @0s Lt Output Signal) is: which becomes when af-"wn, i,.e. when the input signal ;f1;1(t) =x11eat sin w1;` Y v 20 is applied noY more to lters 141 and 11421, -but to filters 141 and 11411 l The inverse Laplace transform (time-expression of the for tO and is equal to zero for t 0 Y y l t 1 The output signal istherefore a signal having w1, as f1' m(t)=`xueae Cos'wlt its carried angular frequency and la waveform limited by 2 1 a steep fron-t and a decreasing exponential slope. 1/ a 25 Let us now consider the lgeneral functions Y wit-.fluff has the dimension of a time and ifjit assumed that a t t (k 1) signal can be neglected when it has fallen under argiven 4 1 r011,152): alt-('k-lfl- T eos 2,1[1- (lc- 1)1] Y fraction of its maximum, say for example 40 db,%00 a-r 0 i l (6) is comprised between two discrete numbers u and (n+1), 1 l, being the number of Sampling periods occupied by an y In these formulae-the rst subscript relates to theV y elementary SignaL central angular 'frequency of the transmitter filter, the The function f1.1(t) may be Written more'generally: 50 Second-Subsl'lpt, after 'a comme, relates to the central v t angular .frequency of the receiver lter and the thi-rd f1:k(f);xk1;k'(z) :(11), subscript, after a semicolon, relates Ito 'the sampling with Y v 1 orde aft-klm k 1 v 2 cyce -r a 1 611310) -e' Sm wilf( 2 The composite signal at tap 61 ata given time instant Y am; being equal to zero for t(k-1)+ 0 fiSr i Y quency significance and refers to the input channel order has a time signicance and refers to theY sampling cycle v 1 t t set up in the ith input channel and in the kth sampling IThis last signal is passed through a receiverrfilter, lter v cycle' gives rise tothe elementary signal f1;1=x1ka1;k(t) 11411 for example, and sampled in sampler -11311 so as At a given instant I thV Ollptltiglll at QFIDHM 121 v to produce sample y11., The value of said sample may of modulator unit101 isthe sum of threeelementary be derived from Equation 7 by adding the intermediary signals: subscript 1 between the two subscripts of the f:

val `r land overlap one another.

Vapply the s arne in series to filter 141 of ,centnal angular 70r y fwz. The resulting'Laplace transform isiY v f 7 In Equations 7 and 8 the time of transit of the elementary signals over common channel 4 lhas been assumed equal to r.

More generally 4if q is the number of a tap ofthe delay line, the sample ym in demodulator 110q is taken up at 5 lthe instant v--l- (q-1)r and ym may be written:

It is to be noticed that, due to the 'mathematical form of the function i aim given by Equation 5, the function remains unchanged 15 when simultaneously the argument is increased by an amount qT and the Athird subscript k is decreased by an integral q. YIn other Words:

aLiHq-DT] @ufff-n+1) 2() awww@ is equal tozero if kq. Thus (9) may be written:

(10) ym: x1ka1,s; kq+1 +x1 k+1)a1,j; kq+2 +xi k+z am kq+a 25 +xzka2,1; k'q+'1 +xz k+1 a2.J; k-q+2 +x2 k+2 a2.i; k-q+a) -lxskaaixk-qm+xa k+1 aa.i: kq+2) Y v +xa k+2 as.1; kq+a 30' In Equation l0 argument T is notwritten but implied. Finally by making k=l, j=l, 2, 3, 11:1, 2, 3, it is found the matricial equation yn i i 3611 i yn @512 3D yla $13 yzr Y 21 yzz :HGHX 3e21 yzs 23 yar 1153i 40 3 /32 '63s ysa w33 where amm (11.1;2 anna (12.1;1 t 112,1;2 02,1;3 01,1-,0 anni 01,1;2 @2,1m 012,1;1 112,1;2 01,1;-1 01.1;0 01,1;1 012,1;-1 (12.1;0 a2.l:1 a4,2;1 0L1.2:2 a1,2;a 02,2;1 02,2;-2 02,2;3 (11) HGH: 04,2;0 a1,2;1l @am @2,2m 02,2;1 @am ,l l11,1;-1 111.2;0 V111,2;1 02,21-1 112,2;0 412,2;1 11;3;1 (11.32 61,353 @2,3m 02,3;2 Claas 111,310 n (11.3;1 111,3;2 a2,3;0 112,3;1 02,3;2 a1,3;-1 @1,310 01,3;1 02,3;-1 112,3;0 412,3;1

Y The general function awk ymay be simplifiedin order to achieve the calculation. The sampling instant t may be so selected that the functionsram-k be maximum. This 55 function being the product of -the two functions 1/2 t e"at andcos wit, one mayselect `for 'maximum of the product the product of the maxima of the two functions.

This gives l l The function amk becomes by stating wi=mx1r and wjl=mrx1r =ek (sin nica-sin mlmr) `which is equal to zero whichever be k.

Further, let us assume that n being even:

That is the minimal frequency spacing 21r- I 2dr between the center frequencies of two adjacent band-lters is equal to l 1 =1 OI :Af-T

then matrix (11) becomes 2 Y 0 l E 0 0 O 0 O V0 0 0 1 0 o 0 0 0` 0 0 0 0 -1 g -z 0 0 0 1 e e 13 (Mlalzaeooo 0-1000 Y 0 0 0 O 0 -1 O 0 0 Y e e o 0A 0 0 0 o 0 0 1 @3.1m Y @3.112 asti-.3 a3,1;o 03,1;1 613,1;2 03.1;-1 (13.1;0 113,1;1 a3.2;1 03,2;2 a3,2;3 a3,2:0 a3.2;! a3.2;2 03,2;-1 @3,2m 113,2;1 @3,3m 113,3;2 113,3;3 113,3;0 (13.3;1 a3,3;2 aaa-1 @3,3mY t13.3;1

which is a'matrix degenerated into three sub-matrices, two of-which are identical, as follows:

Y 2 a @/11 e 6 2 dn511 Y 1 2 Y 1112 5&2 0 1 E X cl2 yl3 0 1 E13 yzi l 11121 1 2 yaz :E 0 "-1 E X U22 1,123 0f Y 0 *1. i623 gai y 1, E E5 Wai 1 1 f A2 y@ 2de .9 1 2 im 333 lo o -1 as,

`minal 2111, a sequence of samples x21, x22, x23

3 9 l By inverting these three matrices, according to Cramers rule (inverse mat1ix=adjugate matrix divided by the determinant of the matrix), one iinds:

Matrix of FIG. 2 has as its `crosspoints resistors' K chronized time base 101 which 'respectively oscillate at which are proportional to the terms of the lirst line of Y matrices (14a) to (14C). In theY simplified case chosen as example, matrix 20 is shown as a detriment in FIG. 5. This' detriment degenerates into three submatrices. It comprises nine tubes 20011 to 20013, 20021 m7201123 and 20031 to 20033 having their grids connected -to the nine inputs ofthe matrix, 11111 to 11113, 11121 to 11123, 11131 to 11133. f Eachtube has an anode resistor andV acathode s resistor so as to operate as a phase-inverter tube` vandV the outputis taken from the cathode load when the term` angular frequencies w1, co2 and w2. Oscillator 311 is connected to two phase-'Shifters 321 and 331 which respectively produce in-phase and phase-quadrature signals. In the lsame way oscillators 312 and 332 are respectively connected to phase-Shifters 322. and 332V and to phase Y Shifters 523 and 333.

As in the case of FIG. 2, common channel 4 is connected to the input of delay line 6 which is provided with three taps 61, 62, 63. Said taps are respectively connected to input terminals 3121, 3122, 3123 of demodulator units 3101,3102,3103. Y Y

Eachl demodulator unit, 2102 forexample, 'comprises six amplitude demodulators 311312, 31312, 311322, 313'22, 31332, 31332. These demodulators may be conventional, of the ring-'type for example. All the demodulators of a given demodulator unit are fed by the elementary signal available at; the corresponding tape of the delay line. Besides, demodulator` 31312 is fed by the output signal of phase-shifter 321, demodulatorV 31312`is fed by the output signal of phase-shifter 331, demodulator 31322 is fed by the output signal of phase-shifter 322,

demodulator 31322is fed by the output signal of phaseshifter 332, demodulator 31332 is fed by the output signal of phase-shifter 323 and demodulator 31332 is fed by the output signal of phase-shifter 333.

of the matrix is positive and from the-anode load when,

`the term of, the matrix is negative. s

Resistors`22011, 22012,` 22013 on the one hand and resistors"22021, 22022, 22023 on the other hand, 22031,

22032, 2203321 least are respectively proportional to 1, t

l and e2='7.389. For example: ,Y Ghms Cathode resistorso the nine tubes T 1000 Anode resistors of the nine"tubes ;A 1 1000 Resistors 22011, 22021, 22031 1-; 100,000 Resistors 22012, 22,022, 22032'. 135,900 Resistors 22013, 22023, 22i"33 ...l.

The voltages across thecrosspoint resistors are added by means of adding resistors 221, `222 andV 223. There is obtained a sequence of samples x11, x12, x13 at terat terminal 2112 and a sequence of. samples x31, x32, x33 at terminal 2113. The sample pulses are demodulated by low-pass lters 2241.3,V i' Y The receiver systemdes'cribed inconnection with FIG. 2 systematicallyl features a desired symmetry vtth respect 3 to the transmitter system illustrated in FIG. 1. It is considered that-such a` representation facilitates a good understanding of the operation ofthe communication system such as 32412 is responsive only t0 input Signals en terwhich essentially comprises, at the transmitting set,

Vchannel and,flat` the'vreceivin'gl set,` delaying` the received 1 -1 elementary signals bysuccessivemultiples, of thesampling period, passingif-the,nondelayed `and delayedfsignalsfY v through reception filters identical to` thel transmission filters, sampling -at the samerate asV in 'the transmitting .To demodulators 31312 and 31312 are connected lowpass filters 32412 and 324'12,l to demodulators 31322 and 31322 are connected lowpass lilters 32422f'and 324'22 fand to demodulators 31332 and 31332 are lconnected lowu pass filters 32432 and 324'32 lThe six filtersv have termillalS 31112 311,121 31122, 31132,

are connected to the input terminals of matrix network V2t) `and respectively correspond to terminal `11112, 11112,

the same operation as a demodular network ofV FIG; `2.v

In the` latter cascfthree subchannels are obtained by separating the input signal on terminal 61' by means of band lters'11411, 11421 and'11431, and each of them in turn provides two separate output signals, one through -an infphase demodulator, the second through a phasequadrature demodulator. There are only two demodulating signals, namely unitimpulses 1572and double unit impulses 153.

Inthe case of FIG'. 4,7separatin'g lters areomitted in the demodulator network, but six-'demodulating-signals Vare provided, which are the" output signals of phase.v

Shifters 321, 331, 322, 332, 323, 3213. 'The operation of the frequency distributiorrof these signals taken by two is thesame as that of .filters 11411, 11421 and 111431.

,Asv arresult ofthe network inFIG. 34, a low-pass-tilter minal 62.111 the frequency band of thegoutput'signal of phase-shiftery 3 21 that is in theV frequency band ofV ijlter 11411. `Synchronized time-base 101'Mand synchronized4 sinusoidal oscillators 311, 312, 313are known in the art. Ex# amples of sinusoidal `oscillators synchronized with a sinusoidal' signal, often called lockedoscillators, are described in the textbookV Pulseand Digital Circuits, by Jacob Millman and-Herbert Tau-b, McGraw-Hill Book Co., Inc.,

paragraph 12;*11, pages 384 to 386` and particularly Fig. v

12.21. They` gener-ally comprise' a stable sinusoidal oscillatordraving*aV tank-circuit, a reactance tubefoonnected across .the oscillatortank and a phasecomparator suitable for comparing the :phases of thersinusoidail signa-l produced by lthe oscillator and thefsynchronizing sinusoidal '75 signal, the 'output' D Crsigna-l` of,A said comparator being used for varying the bias of the reactance tube. A locked oscillator can be used as a frequency divider and when controlled by a nominally sinusoidal synchronizing signal of frequency fs nearly equal to n times (11:21u integer) its natural frequency f1, the oscillator frequency will change from f1 to fs/n and thereafter will run synchronously with the injected signal. Thus a locked oscillator may be easily synchronized at frequencies which are sub-multiples of the frequency of the synchronizing signal.

In the system described in .detail in the foregoing, the

frequency channel overlapping ratio and the ratio be- `tween the elementary signal duration and the sampling cycle duration overlapping ratio were both equal to three. More generally if ,u is the frequency overlapping ratio and 'v the ratio between the elementary signal duration and the sampling cycle duration, there would be fr modulator units such as 101 in the transmitting set of FIG. l, v taps in the delay-line 6 and u filters per each demodulator unit of FIG. 2. The square matrix (ll) would have ,uv lines and columns. As it results from the foregoing, ,u and u are independent parameters since a depends upon both the spacing between the carrier frequencies, that is the center frequencies of the band-filters, and the bandwidths of the same and v depends upon both the attenua'- tion constant of thefilters and the sampling cycle duration. The relations:

which relate the angular carrier frequencies to the sampling period in the embodiment of the invention for which the matrix terms were calculated are only assumed for making easier the calculation of said terms.

What I claim is:

1. A multiplex system comprising means 'for simultaneously and recurrently sampling a plurality of a modu-J Y lation signals and yproducing input recurrent modulated sample pulses, a plurality of ,u first resonant symmetrical band-filter means having center frequencies spaced apart from one another and frequency pass-bands over-lapping one another, said plurality of first resonant symmetrical band-filter means being equal in number to said modulation signal plurality, means for respectively applying said input recurrent modulated sample pulses to sai-d first band-filter means kand deriving therefrom elementary signals, said elementary signals having respectivelyl as their carrier frequencies the center frequencies of said first band-filter means, as their bandwidths the pass-bands thereof and a time-duration comprised between u and (n+1) timesthe recurrence period of said lrecurrent modulated sample pulses, means foradding the elementary signals derived Afrom said first band-filter means and applying the resultant signal .to a single communication channel, a delay line connected to said communication l channel and having taps for distn'buting said resultant signal into v delay line outputs, a plurality of p. second resonant symmetrical band-filter meansrespectively identical to said first resonant symmetrical band-filter means', connected in parallel to each of Vsaid u delay line outputs, means for sampling the output signals of said pv Vsecond resonant symmetrical band-filter means andl deriving therefrom loutput recurrent lsamples whereby said` ,av output recurrent samples are related to ,Lw input samples pulses applied at urecurrent sampling cycles to y. first band-filter means by a matrical constant coefficient relationship,l

. ing a first time-base, a first generator of in-phasefunit pulses anda first generator of phase-quadrature doublet unit pulses drivenby saidvrst timebase ,.means for `apl2 plying to said transmitter a plurality of 2a modulation signals individually issued from independent signal sour-ces, means for simultaneously and recurrently sampling the a modulation` Vsignals from one half of said sources with `the in phase unit pulses and producing input the current modulated sample pulses l.and u modulation signals from the other half of said sources with the phasequadrature doublet unit pulses and producing input recurrent modulated sample doublet pulses, a plurality of /r first resonant symmetrical band-filter means having center frequencies spaced .apart from one another and frequency pass-bands overlapping one another, means for respectively applying said input recurrent modulated sample pulses and said input recurrent modulated sample doublet pulses to said first band-filter means and deriving therefrom elementary signals, said elementary signals having respectively as their carrier frequencies the center frequencies of said first band-filter means, as their bandwidths the pass-bands thereof, a time dur-ation comprised between v and (v-l-l) times the recurrence period of said recurrent modulated sample pulses and sample doublet pulses and the carrier of an elementary signal derived from a sample pulse through a given first bandfilter means being in phase-quadrature with respect to the canrier of an elementary signal derived from a sample doublet pulse through the same first band-filter means, means for adding the elementary signals derived from said firsthand-filter means and applying the resultant signal to a single communication channel and a receiver comprising la second time-base synchronized Vwith the first time-base, a delay line connected to said communication channel and having taps for distributing said resultant signal into v delay line outputs, a plurality of ,usecond f resonant symemtrical band filter means respectively identical to said first resonant symmetrical band-filter means,

'connected in parallel to each of said u del-ay line outputs, -a second generator-of in-phase unit pulses and a second generator of phase-quadrature doublet unit pulses driven Y by said second time-base, means for simultaneously and v recurrently sampling the output signalsof said ,Lw second pling cycles t-o p. first band-filter means by a first matrical constant coeicient relationship, means for simultaneously and recurren-ily sampling the` output signals of said pv second resonant band-filter mean-s by the doublet unit pulses produced by said second phase quadrature doublet unit pulse generator and deriving therefrom output recurrent phase-quadrature samples whereby said ,u1/,output recurrent phase-quadrature samples .are related to ,uv input sample doublet pulses by a second matrical. constant eoefiicientrelationship, a first matrix means having [.w lines connected to said in-phase output sampling means and n columns and crosspoints elements respectively proportional to the coeflicients of said first matrical Vrelationship whereby a first set of a modulation signals are restored at the outputs ofthe columns of said first matrix means and a second matrix means having ,au lines connected to said phase-quadrature output sampling means and p. columns and crosspoints elements' respectively proportional to the coefficients of said second matrical relationship whereby a second set of n modulation signals are restored at the outputs of the columns-of said second matrix means.

3. A multiplex system comprising means for simultaneously and recurrently Vsampling with a recurrence vperiod r a plurality Vof modulation signals and producing input recurrent modul-ated sample pulses, a-plurality of n first resonant symmetrical band-filter means having center frequencies spaced apart from one another by a frequency interval Ynf related to the recurrencelperiodby the `'relationsl'lip 1Af=V2 and v.frequency ypass-bands overlap- 75 ping one another, said plurality Yof first resonant sym- 13 met-rical band-filter means being equal in number to said modulation signal plurality, means for respectively applying said input recurrent modulated sample pulses to said rst band-iilter means and deriving therefrom elementary signals, said elementary signals having respectively as their carrier frequencies the center frequencies of said tir-st band-filter means, as their bandwidths the pass-bands thereof anda time-duration comprised between u Yand (n+1) times the recurrence period of said recurrentV modulated sample pulses, means for adding the elementary signals derived from said first band-tilter means and applying the resul-tant signal to a single communication channel, a delay line connected to said communication Vchannel and having taps for distributing said resultant signal into v delay line outputs, a plurality of n second resonant symemtrical band-filter lmeans respectively identical to said yiirst resonant symmetrical band-filter means, connected in parallel to each of said v delay line outputs, means yfor sampling the V'output signals of said pv second resonant symmetrical band-filter means and deriving therefrom output recurren-t samples whereby ,uw output recurrent samples are related to ,au input samples pulses applied at v recurrent sampling cycles to p. linst band-filter means by a matrical constant coeiiicient relationship, and matrix means having nu lines connected to said second output sampling means and (i columns `and crosspoint elements proportional to said constant coeiicients, whereby the modulation signals are restored at the outputs of said columns.

4. A multiplex system including a transmitter comprising a lirst time-base, a first generator of in-phase unit pulses and a second'generatorI of phase-quadrature doublet unit pulses driven by said rst time-base, means for applying to said transmitter a plurality of 2p modulation signals individually issued from independent signal sources, means forV simultaneously and recurrently sampling with alrecurrence period 'r the ,a modulation signals from one half of said sources with the in-phase` unit pulses and producing input recurrent modulated sample pulses and the ,u modulation signals from the other half of said sources with the phase-quadrature doublet unit pulses and producing input recurrent modulated sample doublet pulses, aplurality of n irst resonantV symmetrical band-lter means having center 'frequencies means, means for adding the elementary signals derivedv from said first band-filter means and applying the resultant signal to a single communication channel and a receiver comprising a second tirne-base synchronized with the rst vtime-base, a delay line connected to said communication channel and having taps for distributing Asaid resultant signal into v delay line outputs, a plurality of ,a second resonant symmetrical band-filter means respectively identical to said rst resonant symmetrical band-iilter means, connected in parallel to each of said l v delay line outputs, a second generator of in-phase .unit pulses and a second generator of phase-quadrature doublet unit pulses driven by said second time-base, means for simultaneously and recurrently sampling the'output signals of the said ,uv second resonant symmetrical bandiilter means by the unit pulses produced by said second in-phase unit pulse generator and deriving therefrom output recurrent in-phase samples whereby said pw output recurrent in-phase samples are related to pv input sample pulses applied at v recurrent sampling cycles to ,u first band-lter means by a first matrical constant coeicient relationship, means for simultaneously Yand recurrently sampling the output signals of said [.w secondV resonant band-filter means by the doublet unit pulses produced by said second phase-quadrature doublet unit pulse generator and derivingtherefrom output recurrent phase-quadrature samples whereby said ,au output recur- Y rent phase-,quadrature samples-are relatedV to 'pv input sample doublet pulses by a second matrical constant coeiiicient relationship, a iirst matrix means having au lines connected to said in-phase output sampling means and ,u columns ,and crosspoints elements respectively proportional to the coefficients of said iirst matrical relationship whereby a irst set of ,a modulation signals are restored at the outputs of the columnsv of said rst matrix means and a second matrix means havingpu lines connected to said phase-quadrature output sampling means and ,n columns and crosspoints elements respectively proportional to the coeiiicients of saidsecond matrical relationship whereby a second set of ,u modulation signals are restored at the outputs of the columns of said second l, References Cited by the Examiner UNITED STATES PATENTS DAVID o, REDINBAUGH, Primm Examinar.r j t 4/53 Dome Y 1799-1555` 

1. A MULTIPLEX SYSTEM COMPRISING MEANS FOR SIMULTANEOUSLY AND RECURRENTLY SAMPLING A PLURALITY OF U MODULATION SIGNALS AND PRODUCING INPUT RECURRENT MODULATED SAMPLE PULSES, A PLURALITY OF U FIRST RESONANT SYMMETRICAL BAND-FILTER MEANS HAVING CENTER FREQUENCIES SPACED APART FROM ONE ANOTHER AND FREQUENCY PASS-BANDS OVER-LAPPING ONE ANOTHER, SAID PLURALITY OF FIRST RESONANT SYMMETRICAL BAND-FILTER MEANS BEING EQUAL IN NUMBER TO SAID MODULATION SIGNAL PLURALITY, MEANS FOR RESPECTIVELY APPLYING SAID INPUT RECURRENT MODULATED SAMPLE PULSES TO SAID FIRST BAND-FILTER MEANS AND DERIVING THEREFROM ELEMENTARY SIGNALS, SAID ELEMENTARY SIGNALS HAVING RESPECTIVELY AS THEIR CARRIER FREQUENCIES THE CENTER FREQUENCIES OF SAID FIRST BAND-FILTER MEANS, AS THEIR BANDWIDTHS THE PASS-BANDS THEREOF AND A TIME-DURATION COMPRISED BETWEEN V AND (V+1) TIMES THE RECURRENCE PERIOD OF SAID RECURRENT MODULATED SAMPLE PULSES, MEANS FOR ADDING THE ELEMENTARY SIGNALS DERIVED FROM SAID FIRST BAND-FILTER MEANS AND APPLYING THE RESULTANT SIGNAL TO A SINGLE COMMUNICATION CHANNEL, A DELAY LINE CONNECTED TO SAID COMMUNICATION CHANNEL AND HAVING TAPS FOR DISTRIBUTING SAID RESULTANT SIGNAL INTO V DELAY LINE OUTPUTS, A PLURALITY OF U SECOND RESONANT SYMMETRICAL BAND-FILTER MEANS RESPECTIVELY IDENTICAL TO SAID FIRST RESONANT SYMMETRICAL BAND-FILTER MEANS, CONNECTED IN PARALLEL TO EACH OF SAID V DELAY LINE OUTPUTS, MEANS FOR SAMPLING THE OUTPUT SIGNALS OF SAID UV SECOND RESONANT SYMMETRICAL BAND-FILTER MEANS AND DERIVING THEREFROM OUTPUT RECURRENT SAMPLES WHEREBY SAID UV OUTPUT RECURRENT SAMPLES ARE RELATED TO UV INPUT SAMPLES PULSES APPLIED AT V RECURRENT SAMPLING CYCLES TO U FIRST BAND-FILTER MEANS BY A MATRICAL CONSTANT COEFFICIENT RELATIONSHIP, AND MATRIX MEANS HAVING UV LINES CONNECTED TO SAID SECOND OUTPUT SAMPLING MEANS AND U COLUMNS AND CROSSPOINT ELEMENTS PROPORTIONAL TO SAID CONSTANT COEFFICIENTS, WHEREBY THE MODULATION SIGNALS ARE RESTORED AT THE OUTPUTS OF SAID COLUMNS. 